lockwood116 15th December 2006, 01:48 PM Hi Woodworkers. I have seen on a metal shaping machine, 220/380 volts. The machine was connected to 3 phase 415 volt supply. What does this mean? Could someone please explain simply.
Lockwood16
bennylaird 15th December 2006, 01:57 PM It's not a simple explanation, but basically the grid consists of 3 supplies which are shifted slighty in phase (relationship to each other).
A normal house uses single phase which is 240V alternating current, a sine wave if you remember your trig.
A three phase connection requires all three to be connected to your house. The 3 phases are used in 3 phase motors etc which when added together provide the same as a 440V supply.
chrisp 15th December 2006, 02:16 PM I'd guess the machine originated from a 220V region of the world. The phase-to-phase voltage of a 3-phase, 220V system is 380V. Therefore I'd guess it is intended for 380V three-phase. The 415V is only 9% higher than 380V so it will probably be okay on 415V. The power will be up by about 20% depending upon the magnetics of the motor.
BTW our voltage will be dropped in the future when we move to 230V (or 400V 3-phase).
lockwood116 15th December 2006, 02:26 PM It's not a simple explanation, but basically the grid consists of 3 supplies which are shifted slighty in phase (relationship to each other).
A normal house uses single phase which is 240V alternating current, a sine wave if you remember your trig.
A three phase connection requires all three to be connected to your house. The 3 phases are used in 3 phase motors etc which when added together provide the same as a 440V supply.
Why do the 3 phases when added together = 420v instead of 660?
bennylaird 15th December 2006, 02:28 PM The phases are separated by 120 degrees.
Hang on I'll find a graphical explanation...........
chrisp 15th December 2006, 02:31 PM Benny,
Its 120 degrees! (3 x 120 deg = 360 deg)
bennylaird 15th December 2006, 02:36 PM Benny,
Its 120 degrees! (3 x 120 deg = 360 deg)
Yes, stuffed up:D
bennylaird 15th December 2006, 02:40 PM OK first up is the measure of volatge. It's in RMS which is root mean square.
A sine wave has an average value of zero as it is positive for 180 degrees then negative for 180.
So we square the instantaneous values of voltage resulting in all values being positive.
We take a mean value of this then take the square root of it.
bennylaird 15th December 2006, 02:42 PM In effect the 240 V single phase goes up to 339V positive and down to 339V negative.
But it's this voltage that produces the same power as a direct current supply ie a battery
bennylaird 15th December 2006, 02:43 PM The pic shows 3 phases and also the 3 phases squared
chrisp 15th December 2006, 03:00 PM It is much easier to talk in phasors (http://en.wikipedia.org/wiki/Phasor_(electronics)#Power_engineering) than in time-domain.
If you accept that one phase is 240V, draw a line on paper from a starting point to 240V on whatever scale you choose. The starting point represents the Neutral, the end of the line represents the RMS voltage of the phase (the length represents the voltage).
Now draw another line from the same starting point but head off 120 degrees from the original line. Again draw it length to 240V.
Do this once more, 120 degrees from the second line. You should have a 3 armed star. Each arm represents a phase.
You can measure the end of each phase to neutral (=240V) and you can measure from the end of one phase to the end of another phase (=415V).
Congratulations, you have now done your first phasor maths problem:)
The maths is now simply trigonometry, but to save you trouble 240V x sqrt(3) = 415V.
bennylaird 15th December 2006, 03:13 PM http://www.elect.mrt.ac.lk/EE201_3phase_sym_comp.pdf
soundman 16th December 2006, 11:54 PM welcom to the globalised australia..... the standard power point voltage is now nominaly 230V.... they've fiddled with the tolerances too which makes it easier for the power generators....... another instance of legeslated lowering of the bar on service and quality.
remember 240 v between phase and neutral ( and earth)
415v between any two phases.
Its magic.
cheers
ian 16th December 2006, 11:59 PM welcom to the globalised australia..... the standard power point voltage is now nominaly 230V.... they've fiddled with the tolerances too which makes it easier for the power generators....... another instance of legeslated lowering of the bar on service and quality.and here was I believing it was about dropping our voltage so that euro appliances (implies a greater number of manufacturers and models) would work in good old OZ.
of course I'm not sure a euro spec fridge will work through an Australian summer!!
another reason most new houses are air conditioned ??
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